Advice for maybe snaking a septic tank or d-box...

I have a septic tank in a yard that deals with high water tables every winter. I have spent a lot of time and money of the last few years keeping as much water out of the drain field as possible to keep thing healthy.. I installed a french drain system in part of the yard that used to puddle; I also installed underground pipes to catch rain from our roof and dump it into a sump hole which then pumps the water to a street drain - bypassing the drainfield.

In 2010 -- before the above was installed -- we had a bad experience with the yard flooding and toilets and whatnot draining very slowly. We called out a septic company and long story short, they pumped the tank, dug up the distribution box, vacuumed the lines (blown baffle so there was sludge in the pipes) and then sent cameras through all of the leech pipes. the result was a lot of money but they told us the lines were healthy and everything looked good. They installed risers so it would be easier to pump next time.

Now here is my current problem: It has been raining a lot of course, but my yard (drainfield) is not overly saturated. lat night my downstairs toilet closest to the tank (15' away) wouldn't accept a flush. The water level wold rise hi8gh like there was a clog, then verrrrrry slowly go down, but not take away much of what was in the bowl. It would also not fill the bowl again, so there would just be a small amount of liquid in the bottom of the toilet. I peeked outside and saw that the riser for inspecting the outlet baffle is allowing the effluent to overflow onto the grass creating a small puddle around the risers. Keep in mind, the rest of the yard is not saturated. My wife has been watching it all day and keeping any water use to a minimum. She said at one point the puddles went away, but then she later they were back.

Here is my ignorant hypotheses: I think there is a clog from the outlet between the tank and the distribution box so the flush goes into the tank, then can't get to the d-box and the drainfield. The folks who came out in 2010 installed a new baffle at that outlet that goes to the d-box, but they did not install a filter. I am just not sure how to diagnose if my idea is correct. Should I dig up the distribution box and look? Or take a long rod and gentle prob around the baffle to see if there are any obstructions. or neither?

Also, There seems to be a cleanout-looking pipe thing in the same bathroom as the no-flushing toilet. I can probably open it, but I am afraid water might shut up through it so I haven't done it yet. It sticks up about 10" above the level of the floor about 2' closer to the septic tank than the toilet.

I hope this all makes sense. I can't afford to have a bunch more expensive stuff done on my septic. Any help or advice would be greatly appreciated.